Files: Simplify duplicate name management

[tintou]

(From https://github.com/elementary/files/pull/1437)
We want to end the overly complicated handling of duplicates to a simple one.
For links:

• FileName (link)
• FileName (link 2)
• etc.

For copies

• FileName (copy)
• FileName (copy 2)

[jeremypw]

https://github.com/elementary/files/pull/1437 is waiting to be amended along these lines - but I rather forgot about it.

[jeremypw]

One question - if you copy Filename (link) should you get Filename (link)(copy) or Filename (link 2)? Unlikely to be an issue in practice I imagine.

[tintou]

I imagine that you get Filename (link 2) as it is more a second link than a copy :man_shrugging:

[jeremypw]

Regarding copies of filenames with extensions, I imagine you want BaseName (copy).Extension as at present.

[jeremypw]

There are some complications with copying or linking file copies or links which are already named in the old format but I will not address that in the first PRs.